Abstract:A steel rail, severely gouged during a rocket-sled test, was the focus of an investigation of the microstructural changes which occur during high-velocity, sliding contact. Metallographic analysis of the damaged rail indicated that the mechanism of gouging probably was a crude machining process in which the sled shoe played the role of a tool. Cracks in bands of martensite and severely distorted pearlite regions were the principal microscopic features of the subsurface damage; the overall configuration of the pattern of cracks and martensite bands suggests that they formed as a result of catastrophic thermoplastic shear